1. Field of the Invention
The present invention relates generally to wireless communication systems and, more particularly, to wireless communication system transceivers.
2. Description of the Related Art
Conventional local oscillators for communication systems, whether wireless or otherwise, have typically been realized with a) oven-controlled crystal oscillators or b) voltage-controlled oscillators with Costas loops in order to maintain precise (e.g., nanosecond accuracy) timing of local oscillator signals for upstream and downstream applications. Although these local-oscillator structures can generate suitable downconverting and upconverting signals, they are generally expensive. In addition, they are typically large so that they consume an undue amount of circuit board real estate.
The present invention is directed to small, inexpensive local-oscillator systems that provide stable, phase coherent local-oscillator signals for conversion of downstream communication signals to downstream data signals and a corresponding bit timing clock and conversion of upstream data signals to upstream communication signals.
Local-oscillator systems of the invention are realized with oscillator networks that are phase locked to the bit timing clock. Two of the networks provide first and second phase coherent local-oscillator signals respectively to a receiver and transmitter of a communication transceiver. A third oscillator system forms a phase lock loop about one of the other networks and preferably includes a crystal to enhance short term stability.
Because they track the phase of the bit timing clock, the frequencies of the first and second local-oscillator signals have fixed relationships to the frequency of the bit timing clock and because the bit timimg clock is derived from downstream communication signals that originate in a communication system""s head end, the first and second local-oscillator signals insure phase coherency between the upstream and downstream communication signals.
Local-oscillator methods are also provided and communication systems are shown that include the local-oscillator systems.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.